For the last two decades, the main criterion for VLSI circuit design has been high performance. Small area and low-power dissipation have been secondary considerations. Recently, the increasing demand for battery powered systems like mobile computers, personal communications services (PCS) and wireless communications systems has shuffled this order of importance, making low-power design the most important criterion. This is a result of the fact that battery operating time of any portable system is a very important parameter. Unfortunately, improvements in battery design have not been rapid enough to accommodate the increasing power demands of high performance systems.
Another reason for the increased importance of low power in VLSI design is the continuous reduction in transistor sizes which allow the integration of larger numbers of transistors in smaller areas. Increasing the number of transistors per unit area increases heat dissipation and chip temperature which in turn reduces the reliability of semiconductor chips. Since the ability to sink heat per unit area is limited and very expensive to increase in terms of size and cost, this increasing temperature establishes an upper bound on the maximum number of transistors per unit area.
Many techniques have been developed for low power design such as described in Bellaouar and M. I. Elmasry, "Low-Power Digital VLSI Design", Keluwer Academic Publishers, 1995, and P. Chandrkasan, S. Sheng and R. W.
Brodersen, "Low-Power CMOS Digital Design". Most of these techniques sacrifice performance to reduce power consumption. Generally, design for low power conflicts with design for high performance because the latter normally requires higher supply voltages, current sources and larger transistors.
According to the present invention, a Dynamic Current Mode Logic (DyCML) circuit is provided which achieves high-performance at low-voltage and low-power consumption. The DyCML logic circuitry of the present invention enjoys certain features of MCML circuits, such as high performance and noise immunity, without sacrificing static power and without requiring a large area for load resistors.